The real issue, as you noted, is the FFL problem and interstate shipment of ammo and firearms.
I think the only legal solution to that issue is having the states start creating a semi-organized militia-- if you have the equivalent of CCW training, you can get what you want from a state armorer.
The state buys the firearms and sells them to you as a militia member, possibly using existing FFL holders as the base of armorers.
Of course, when the BATFE swoops in they'll have to be stopped by state or local law enforcement. Or the local militia.
Better on that: the state can then authorize members to buy new (yes, post-’86) machine guns for themselves. It’s a loophole in 922(o).
(I have a theory some very high politicians own, themselves, new machine guns. It’s legal with the right connections, which they keep very quiet.)